Field of the Invention
The invention relates to a device for correcting skewed sheets in a feeder of a sheet-fed printing press, the device, more particularly, having at least one sucker which is adjustable in height and is disposed on a driven movable sucker carrier for horizontally transporting and simultaneously aligning a sheet lifted from a sheet pile, the sucker carrier being articulatingly connected to a rocker arm which is mounted in a frame of the printing press so as to be movable in a feeding direction of the sheet and swingably driven, the sucker carrier being braced against a cam guide which is adjustable in height.
Such a device is intended to provide an accurate alignment of the sheet while it is yet on its transport path from the sheet pile toward the front or side lay marks or some other transport means for further conveyance or feeding of the sheet, in order thereby to enhance the reliability of the sheet alignment, especially at high printing speeds and/or with sensitive or delicate printing materials or stock. Various devices have therefore been provided by which the sheet, on its transport path toward the front lay marks or toward the transport means which further convey or feed the sheet, is rotated slightly about its vertical axis depending upon how skewed it is, and is thus aligned with its leading edge precisely perpendicularly to the direction of conveyance or feeding.
The device described in generic terms in the introduction hereto is the device heretofore known from its use with the conventional so-called "RYOBI 520" sheet-fed printing press. In this heretofore known construction, the correction of a skewed sheet is effected by changing the location of the rocker arm by means of an adjusting screw with an adjusting wheel, the latter moving constantly with the rocker arm. For kinematic reasons, this change in the length of the rocker arm also changes the height of the sucker. Intrinsically, the height of the sucker is adjusted by an adjustment of the scanner switch of the device for tracking the stack of sheets to be worked through. It has been found to be disadvantageous, if an intentional increase in spacing between the sucker and the surface of the sheet pile is effected so as to avoid the feeding of double sheets, that the sheet-pile table must be lowered a desired amount after the adjustment has been made. Only in this way can the spacing sought-after become effective.
In a different type of sheet-fed printing press, a sucker transmission is used having two cam disks which, on the one hand, in cooperation with the cam segment, control the sucker stroke and, on the other hand, control the horizontal transport movement. Due to a coordination of these two am roller movements, a desired guidance of the sucker is provided. An adjustment of a kinematic dimension would necessarily affect both partial movements, a result which is undesired
German Patent 11 77 652 describes a device for correcting skewed sheets, wherein two suction nozzles are swivellable in common, by the action of a control cam, about a shaft which is swingably moved by a second control cam. In order to effect an acceleration or deceleration of a suction nozzle, this suction nozzle is rotatably mounted and is disposed so as to swivellable about a stationary pivot axis under the influence of an adjustable connecting rod during the transport movement. This swivelling motion of the one nozzle is achieved by means of a lever which is connected to a tie rod having an end thereof rotatable about a pin or trunnion, and this pin or trunnion can be adjusted by an adjusting device towards both sides by the shaft of a connecting rod carrying the nozzles.